Fillers of inorganic material typically are added to cellulose fibers during alkaline paper making to improve brightness, opacity, paper smoothness, and/or printability. Fillers used in alkaline paper making processes generally are inorganic materials. As much filler as possible is employed in manufacture of alkaline paper because increasing the amount of filler in alkaline paper making reduces manufacturing costs. Additionally, the filler provides improved properties to alkaline paper such as opacity and brightness.
Brightness is a function of light reflectiveness. Inorganic materials such as chalk, talc and clays provide low brightness. It is known that the brightness imparted by filler clays can be improved through calcination. However, calcined clay is undesirably abrasive.
The brightness of alkaline paper that contains inorganic fillers which have low brightness also can be improved by including fluorescent whitening agents or optical brighteners. However, these chemicals are expensive and present environmental concerns.
The art shows various filler materials and processes for paper making. U.S. Pat. No. 2,795,509 discloses stable dispersions of silicon dioxide in solutions of cellulose ethers which are useful as sizing compositions.
U.S. Pat. No. 3,730,830 discloses a method for making paper having good strength wherein a slurry of staple fiber, carboxymethylcellulose and an inorganic pigment is formed, followed by addition of cellulose fiber.
U.S. Pat. No. 4,310,360 discloses a method for producing a sizing composition comprising heating a pigment in the presence of a polysaccharide.
U.S. Pat. 4,210,488 discloses a process for improving the effect of optical brighteners by absorbing polypiperdine halide adsorbed on carboxymethylcellulose.
Carboxymethylcellulose is a wet end paper additive which improves the dry strength of paper. Solutions of carboxymethylcellulose can also be applied to the surface of paper to improve surface strength, smoothness, as well as oil or grease holdout.
None of the above patents successfully address the problem of improving the brightness of alkaline paper products which contain inorganic pigment type fillers. Accordingly, a need exists for an inorganic filler material that provides increased brightness in alkaline paper products.